The present invention relates to a sensor for detecting the direction of a magnetic field. More specifically, it relates to a magnetic direction sensor adapted to detect the direction of a weak magnetic field such as a geomagnetism.
Recently, attempts have been made to provide a vehicle with apparatus for indicating the direction of the vehicle by detecting the direction of a geomagnetism, or with a system called trip computer which treats information including the vehicle's velocity, direction and place to give to a driver information concerning the distance to the destination, etc. In order for a vehicle to reach the destination without fail, exact detection of the direction of a magnetic field is critical.
Conventionally as direction sensors which detect the direction of geomagnetism, those using hole elements (see Japanese Patent Laid-Open No. 56-143905) and those comprising rotating magnetic cores (see Japanese Patent Laid-Open No. 57-76411) are known. However, the direction sensor using a hole element suffurs from a low sensitivity, and its characteristics are largely changeable due to moisture variation and large differences in characteristics from one hole element to another. Moreover, the direction sensor comprising the rotating magnetic core is complicated in mechanism, so it is not suitable for miniaturization, leaving it expensive. Therefore, these sensors have failed to find a wide commercial use.
To solve the problems of the above-mentioned conventional direction sensors, a so-called ring core-type magnetic direction sensor has recently been proposed. It comprises an annular magnetic core formed by winding a ferromagnetic metal ribbon, a winding for exciting the magnetic core, a pair of output windings each wound about the magnetic core such that it encircles the opposite portions of the magnetic core, the two output windings being arranged perpendicular to each other so that they provide output signals to determine the angle between the magnetic core and an external magnetic field. See Japanese Patent Laid-Open No. 54-21889 and IEEE Transaction on Geoscience Electronics, Vol. GE-7, No. 4, Oct. 1969, etc.
The magnetic direction sensor of this ring core type is relatively good in detection sensitivity. Its structure is simple and its detection head can be made compact. Further, its subsequent signal-treating circuit is relatively simple. As a result, the overall apparatus for detecting the direction of a magnetic field is expected to become compact and less expensive.
When the magnetic direction sensor was to be constructed by using a magnetic core formed by winding a ferromagnetic metal ribbon, it was conventionally considered that every part of the magnetic core should have as uniform a cross section as possible to ensure that every part of the magnetic core is subjected to the same magnetic flux .phi.. Specifically speaking, when the metal ribbon was wound in a toroidal shape, both inner and outer ends of the metal ribbon were arranged essentially along the same radius of the core. In other words, they were terminated circumferentially at the same position. Further, since the same positioning of both ends of the metal ribbon is not always achieved in an industrial mass production, attempts were made to use an extremely thin ferromagnetic metal ribbon to ensure a minimum change of the cross section of the resulting magnetic core.
Nevertheless, such direction sensors are not necessarily satisfactory with respect to a detection accuracy, which has been a big obstacle to the commercial use of such sensors.
Furthermore, a magnetic direction sensor head having the magnetic core constructed by permalloy ribbon has magnetic characteristics which are likely to change under the influence of vibration, external force, etc. because permalloy's magnetic characteristics are generally highly affected by deformation. This seems to make it further difficult to pinpoint the exact causes of poor accuracy in detecting the direction of a magnetic field.